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won't start on foggy mornings

1K views 17 replies 7 participants last post by  Bill Kapaun 
#1 ·
Last season my riding mower, which is a Craftsman YT3000 with a 21 HP Briggs & Stratton, began taking two or three cranks to spark and start up.

We have had a warm winter, and it began refusing to start when the temperature is below freezing. The mower is about three/four years old so I assumed the battery. The battery tester showed the battery to be fine, but I replaced it with a known good battery, though the problem with starting up has continued. On warm (above freezing temperature) days it starts up.

One morning it was 40 degree (F) out, and foggy. It would not start. Tried a couple times, then waited until about 1/2 hour after the fog cleared and it started up. This reminded me of a recent day, it had finished raining and I don't do anything in the yard after a rain but I did want to drive the mower into the garage to work on it, and it would not start.

What could prevent the mower's engine from starting when temperature is below freezing or above freezing temperature and there is high humidity?
 
#2 ·
Perhaps the spark plug wire(s) have developed cracks in the insulation,allowing the high voltage spark to jump to ground thru the easiest path,rather than firing the spark plugs..
The ignition coil may have a crack or its windings exposed,that allows moisture to get in it and do the same thing ..once it dries off it'll usually work ok again ,at least temporarily..

The plug wires may be integral with the ignition coil--not sure if new ones can be put on ,or if the whole unit has to be replaced..

It could be a fuel issue but most of the cases when moisture is involved it a spark problem..
 
#3 ·
Carburetor icing... The humidity in the air (the fog) and the near-freezing temperatures are the key here. Air enters your carburetor, into the throat of the carb, aka the venturi (the passage where the air and fuel are mixed) the air is sped up, by the Venturi principle. However, the other effect of the Venturi principle is that the temperature is lowered, causing the the moisture in the air to condense out and freeze inside the venturi. A very common problem in older carbureted cars (I had the issue with my 78 Fairmont) and older carbureted aircraft. The solution in my car was to let it idle until the engine was warmed up enough that it would heat up the carb enough to prevent icing. Not sure what the solution is for your tractor, try to keep the carb warm at initial idle I guess.
 
#5 · (Edited)
I have a vague recollection of this topic coming up before, I'll try to find that thread for you. I kinda remember something about someone using a hair dryer to heat their carb before starting, but that one is really hazy. And I am definitely not recommending swiping your significant other's hair dryer for this purpose. Heat gun might be a little excessive too, considering you'd be pointing it at someplace filled with combustible material... Safety first!

Here's one....

http://www.mytractorforum.com/12-john-deere-forum/523330-can-somebody-explain-icing.html

And I went back and read through this one,

http://www.mytractorforum.com/12-john-deere-forum/496314-lx176-no-start-2.html

which was the hair dryer one, and the first issue in the thread turned out to be a bunged up carb, but the second person along with a similar issue had carb icing issues. Could be both, I guess, a fuel delivery issue that is exacerbated by low temperatures and humidity in the air. Do you find (when you start it up and it actually runs) that you have to leave the choke on for quite some time before your machine runs happily?
 
#7 ·
Not much to go on, but I'd suspect the choke isn't closing fully. Easy and quick to check it out.
 
#8 ·
Do you have an inline spark tester to see if you are getting spark when cranking?
Run it sometime in the dark and look for any sparks jumping to chassis from the plug wire.
 
#9 ·
littletractorguy asked:
> Do you find (when you start it up and it actually runs) that you have to
> leave the choke on for quite some time before your machine runs happily?
No. Once it sparks it starts up. Well, I guess technically I cannot see
or hear a spark. Once I hear it pop from combustion, the next time I turn
the ignition it starts up and runs fine.

So, I only noticed this problem once the temperatures were still below
32 degrees in the late mornings. So like a few weeks ago, we had that
warm weather, and I would go out saturday morning and after sitting all
week and two turns of the ignition and it starts up. Go out the next
morning and it starts up on the first turn of the ignition.
The previous two weeks have been freezing, and the mower has been sitting
unused for two weeks, so on the fourth turn of the ignition I finally
hear the pop and the fifth is starts.



Bill Kapaun asked:
> Does it not crank fast enough or what?
Mmmm, I am not sure. Until this issue came up I did not really pay that much
attention to how it cranked before. My impression is that it is struggling a
bit more to turn over.



PaulL asked:
> Do you have an inline spark tester to see if you are getting spark when cranking?
I do not. I will need to get one. Are they universal, or would there be a particular
size I need to get for the type of spark plug my mower uses (RC12YC)?



Fcubman said:
> Not much to go on, but I'd suspect the choke isn't closing fully.
This might be related. The mower started smoking (early last year).
I took it to a local mower repair shop.
They charged me for a new head gasket.
Got it back, still smoking.
Wasted money, not going there again.
Turned out that the muffler was damaged.
Fixed that, but some smoke was still coming out for the first minute.
Turned out that when they put the mower engine back they did not reseat
the breather tube correctly. I had been running it for a while before
I figured that one out.
 
#10 ·
.....snip
So, I only noticed this problem once the temperatures were still below
32 degrees in the late mornings
.......


Bill Kapaun asked:
> Does it not crank fast enough or what?
Mmmm, I am not sure. Until this issue came up I did not really pay that much
attention to how it cranked before. My impression is that it is struggling a
bit more to turn over.
Engines crank slower in cold weather.
Oil is thicker and the available battery voltage/amperage is less.

IF your battery is a couple years old, it may simply be borderline for the task at hand.
An auto parts store can load test it for free.

Briggs OHV engines require the valve lash to be correct for the automatic compression release (ACR) to work. If the lash is too much, the engine can be much more difficult to turn over. Add cold weather, a battery that might be a bit weak and the cumulative effect is NOT UNEXPECTED.

You STILL haven't stated what the craftsman 917.xxxxxx number is.
Apparently you don't think it matters to provide more complete info?
 
#11 ·
#15 ·
A lot of good advice. I'll throw in a penny's worth or two.
Make sure the battery is fully charged, it should have volts above 12.5 for a good charge.
If the sparks get weak or quit when it is damp out - rainy, foggy, drizzly, etc - then you can check for secondary (fat) spark plug wire leaking the spark through faulty insulation, or insulation that absorbs moisture while sitting, and burps it up when it gets hotter/drier.
If it has faulty insulation that is moisture sensitive, you can dry it out in a warm oven(don't tell Mom), and then spray the insulation with Krylon clear or any other coating that will keep the moisture out, and not conduct the electricity of the spark. Let that dry, re-install, and it should be good for a few more years.
YOu can also wipe off the ceramic portion of the spark plug, especially if it has oil or other coating, or is damp, as damp combined with dust may for a shorter/easier way for the spark to jump to ground. Just remove the socket, and wipe the ceramic with a clean dry cloth, re-install the socket, and twirl away.
The ACR - Automatic Compression Release - allows a bit of the gas/air mix to escape past a valve on the compression stroke of a cranking engine. At higher-than-cranking rpms, the ACR quits doing that, and allows the full, inducted, fuel-air charge to be compressed. With less in the cylinder,(some escaped...) the starter motor finds it easier to compress, and there is enough to get the engine running.
If the valve lash - clearance between the valve stem (tip of the valve) and the rocker arm or tappet- is too tight, the valve 'tulip' cannot seat tightly, and may cause compression problems, or damage to the valve as it cannot transfer heat from the valve (exhaust valve has burning gas streaming past on the way out - 100% hot) to the valve seat, which transfers the heat to the fins, which are cooled by the blower on the crankshaft. The intakes have cool fuel:air coming in all the time, so are less sensitive to 'too close' adjustments. If the intake valve is too loose, then the ACR cannot 'bump' the valve to allow a bit of the mix to escape, as it won't take up that much slack in the adjustment, and you'll lose ACR, and the starter motor will GROAN trying to start, possibly easing past the compression stroke, and maybe firing on the next. Or not.
tom
 
#16 ·
Thank you for all the replies so far.
I have been busy with other stuff.
I ordered a spark tester and plugged it in on the mower.
The other night I verified it is sparking.
The mower has been sitting for some time now (two weeks???), and I have noticed that even though it starts in warm/dry weather it takes longer... maybe as if some sort of fluid is settling between uses? If it is only sitting for a day or two it starts up quickly, if a week to two weeks I have to hold the starter down for two full seconds before it starts.

So two weekends ago, I cleaned off the engine, muffler and other parts. Yesterday I was looking it over and there were three or four drops worth of oil on the muffler, and I can see that the engine is leaking somewhere to the front of the mower... which is where I think the head is.

I will check out the other stuff as I get time. I have a battery tester and charger, I have been keeping it charged even if it doesn't need it, so the battery is fine.
 
#18 ·
Thank you for all the replies so far.
I have been busy with other stuff.
I ordered a spark tester and plugged it in on the mower.
The other night I verified it is sparking.
The mower has been sitting for some time now (two weeks???), and I have noticed that even though it starts in warm/dry weather it takes longer... maybe as if some sort of fluid is settling between uses? If it is only sitting for a day or two it starts up quickly, if a week to two weeks I have to hold the starter down for two full seconds before it starts.

So two weekends ago, I cleaned off the engine, muffler and other parts. Yesterday I was looking it over and there were three or four drops worth of oil on the muffler, and I can see that the engine is leaking somewhere to the front of the mower... which is where I think the head is.

I will check out the other stuff as I get time. I have a battery tester and charger, I have been keeping it charged even if it doesn't need it, so the battery is fine.
2 seconds is diddly squat.
Don't worry about it. These aren't computer controlled automobile engines!
 
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